J.A. van der Goot

Extended-spectrum-β-lactamase- and AmpC-β-lactamase-producing Escherichia coli in Dutch broilers and broiler farmers

OBJECTIVES The aim of this study was to establish the prevalence of extended-spectrum β-lactamase (ESBL)- and AmpC β-lactamase-producing Escherichia coli at Dutch broiler farms and in farmers and to compare ESBL/AmpC-producing isolates from farmers and their animals. METHODS Twenty-five to 41 cloacal swabs collected from broilers at each of 26 farms and 18 faecal samples from 18 broiler farmers were analysed for determination of the presence of ESBL/AmpC-producing E. coli. ESBL/AmpC genes were characterized by microarray, PCR and sequencing. Plasmids were characterized by transformation and PCR-based replicon typing. Subtyping of plasmids was done by plasmid multilocus sequence typing or restriction fragment length polymorphism. E. coli genotypes were determined by multilocus sequence typing. RESULTS Birds from all farms were positive for ESBL/AmpC-producing E. coli, and on 22/26 farms the within-farm prevalence was ≥ 80%. Six of 18 farmers carried isolates containing ESBL/AmpC genes bla(CTX-M-1), bla(CMY-2) and/or bla(SHV-12), which were also present in the samples from their animals. In five of these isolates, the genes were located on identical plasmid families [IncI1 (n = 3), IncK (n = 1) or IncN (n = 1)], and in isolates from two farmers the genes were carried on identical plasmid subtypes (IncI1 ST12 and IncN ST1, where ST stands for sequence type) as in the isolates from their animals. CONCLUSIONS This study shows a high prevalence of birds carrying ESBL/AmpC-producing E. coli at Dutch broiler farms and a high prevalence of ESBL/AmpC-producing E. coli in farmers. This is undesirable due to the risk this poses to human health. Future research should focus on identification of the source of these isolates in the broiler production chain to make interventions resulting in reduction of these isolates possible.

Comparison of the transmission characteristics of low and high pathogenicity avian influenza A virus (H5N2).

Low pathogenicity avian influenza A strains (LPAI) of the H5 and H7 type are noted for their ability to transform into highly pathogenic counterparts (HPAI). Here we compare the transmission characteristics in poultry of LPAI H5N2 (A/Chicken/Pennsylvania/83) and corresponding HPAI virus by means of transmission experiments. In the experiments, five inoculated animals are placed in a cage with five contact animals, and the infection chain is monitored by taking blood samples, and samples from the trachea and cloaca. The data are analysed by final size methods and a generalized linear model. The results show that HPAI virus is more infectious and induces a longer infectious period than LPAI. In fact, fully susceptible animals are invariably infected when confronted with HPAI virus and die within six days after infection. Animals previously infected with LPAI virus, on the other hand, survive an infection with HPAI virus or escape infection all together. This implies that a previous infection with LPAI virus effectively reduces susceptibility of the host to infection and decreases transmission of HPAI virus. We discuss the implications of these conclusions for the control and evolution of avian influenza viruses.

Effect of Vaccination on Transmission of HPAI H5N1: The Effect of a Single Vaccination Dose on Transmission of Highly Pathogenic Avian Influenza H5N1 in Peking Ducks

Abstract The highly pathogenic H5N1 avian influenza virus is widespread among domestic ducks throughout Southeast Asia. Many aspects of the poultry industry and social habits hinder the containment and eradication of AI. Vaccination is often put forward as a tool for the control of AI. However, vaccination will only lead to eradication when it reduces the virus spread to such an extent that herd immunity is obtained. To study the effect of a single vaccination dose on the transmission of H5N1 in domestic ducks we performed experiments in which infected and uninfected ducks were housed together and the infection chain was monitored by means of virus isolation and serology. Specifically, Peking ducks were vaccinated with A/Chicken/Mexico/232/94/CPA H5N2 and challenged with A/Chicken/GxLA/1204/04 H5N1 one week after vaccination. In both the control and vaccinated groups all inoculated and contact animals were quickly infected. However, the disease signs and mortality differed between the control and treatment groups. This finding may have important implications for the control of H5N1 by means of vaccination.

Transmission between chickens of an H7N1 low pathogenic avian influenza virus isolated during the epidemic of 1999 in Italy.

The transmissibility of an H7N1 Low Pathogenic Avian Influenza (LPAI) virus isolated from a turkey flock during the large epidemic in Italy in 1999, was experimentally studied in chickens. Four group transmission experiments were performed. Infection and transmission were monitored by means of virus isolation on swab samples and antibody detection in serum samples. From the results of these groups, we estimated the mean infectious period at 7.7 (6.7-8.7) days, the transmission rate parameter at 0.49 (0.30-0.75) infections per infectious chicken per day and the basic reproduction ratio at 3.8 (1.3-6.3). These estimates can be used for the development of surveillance and control programmes of LPAI in poultry.

Using egg production data to quantify within-flock transmission of low pathogenic avian influenza virus in commercial layer chickens

Even though low pathogenic avian influenza viruses (LPAIv) affect the poultry industry of several countries in the world, information about their transmission characteristics in poultry is sparse. Outbreak reports of LPAIv in layer chickens have described drops in egg production that appear to be correlated with the virus transmission dynamics. The objective of this study was to use egg production data from LPAIv infected layer flocks to quantify the within-flock transmission parameters of the virus. Egg production data from two commercial layer chicken flocks which were infected with an H7N3 LPAIv were used for this study. In addition, an isolate of the H7N3 LPAIv causing these outbreaks was used in a transmission experiment. The field and experimental estimates showed that this is a virus with high transmission characteristics. Furthermore, with the field method, the day of introduction of the virus into the flock was estimated. The method here presented uses compartmental models that assume homogeneous mixing. This method is, therefore, best suited to study transmission in commercial flocks with a litter (floor-reared) housing system. It would also perform better, when used to study transmission retrospectively, after the outbreak has finished and there is egg production data from recovered chickens. This method cannot be used when a flock was affected with a LPAIv with low transmission characteristics (R(0)<2), since the drop in egg production would be low and likely to be confounded with the expected decrease in production due to aging of the flock. Because only two flocks were used for this analysis, this study is a preliminary basis for a proof of principle that transmission parameters of LPAIv infections in layer chicken flocks could be quantified using the egg production data from affected flocks.